fix(utils): make clone() only copy own properties

Re: Automattic/mongoose#9876

lib/utils.js

@@ -68,9 +68,8 @@ exports.cloneObject = function cloneObject(obj, options) {
   var ret = {};
   var hasKeys;
   var val;
-  var k;
 
-  for (k in obj) {
+  for (const k of Object.keys(obj)) {
     // Not technically prototype pollution because this wouldn't merge properties
     // onto `Object.prototype`, but avoid properties like __proto__ as a precaution.
     if (specialProperties.indexOf(k) !== -1) {
@@ -295,13 +294,7 @@ exports.isArray = function(arg) {
  * Object.keys helper
  */
 
-exports.keys = Object.keys || function(obj) {
-  var keys = [];
-  for (var k in obj) if (obj.hasOwnProperty(k)) {
-    keys.push(k);
-  }
-  return keys;
-};
+exports.keys = Object.keys;
 
 /**
  * Basic Object.create polyfill.